In particular, machine tools, production machines, transportation machines and/or handling machines are frequently powered by means of electrical synchronous motors. In such applications the machines have a number of driving axles, which are each powered by means of an appropriate synchronous motor.
Operation of such a machine generally requires the positions of the rotors of the synchronous motors and thus the mechanical angle of rotation of the motor shafts to be synchronized with one another so as to synchronize the driving of the different belts used for transporting a product in a transportation machine for instance.
FIG. 1 shows a drive system generally known from the prior art for operating a synchronous motor 1. The synchronous motor 1 has a motor shaft 2, which is connected to a rotor 3 of the synchronous motor 1 in a torque-proof manner. The motor shaft 2 powers a load 10, which can be present in the form of a drive roller for powering a conveyor belt for instance. A position sensor 4, which is connected to the motor shaft 2, measures the position α of the rotor 3, i.e. in the case of a rotatory synchronous motor, the mechanical angle of rotation α of the rotor 3, which corresponds with the angle of rotation of the motor shaft 2. The position α of the rotor 3 thus determined is usually fed to a closed-loop control device 8 as an input variable. By deriving the position α according to the time t and dividing by the value 2π, the closed-loop control device 8 calculates an actual speed value and subtracts this from a predetermined speed set point fsoll. The difference thus determined is then fed to a proportional integral controller as an input variable for instance, within the closed-loop control device 8, said input variable outputting a speed f as an output variable. The speed f determined in such a manner by the closed-loop control device 8 is usually fed to a rotation angle determination unit 6 as an input variable, which calculates an electrical angle of rotation α′ of a voltage vector according to the equation:
                    α        ′            ⁡              (        t        )              =                            ∫                      t            =                          t              0                                t                ⁢                  2          ⁢          π          ⁢                                          ⁢                      f            ⁡                          (              t              )                                ⁢                                          ⁢                      ⅆ            t                              +                        α          ′                ⁡                  (                      t            0                    )                      ,
t: time
t0: starting time
with a modulo calculation for restricting the angle α′ to the value range−π<α′≦π
when α′<−π, then α′:=α′+2π and
when α′>π, then α′:=α′−2π
additionally being carried out. The electrical angle of rotation α′ of the voltage vector 13 is shown here in FIG. 2. The electrical angle of rotation α′ determined in such a way is fed to a converter unit 5 as an input variable, which generates the three output voltages U1, U2, U3 for activating the synchronous motor 1 from the electrical angle of rotation α′ with the aid of an integrated converter. To this end, the converter unit 5 is connected on the output side to the synchronous motor via lines 12.
In general, the converter unit 5 and the rotation angle determination unit 6 are usually integrated within a driving facility 7, which can take the form of a SINAMICS S120 for instance, developed by Siemens. The closed-loop control device 8 usually forms part of a computing apparatus 9, which can generally be present in the form of a numerical open-loop and/or closed-loop control, such as for instance a SIMOTION D4X5, developed by Siemens. The position sensor 4, the closed-loop control device 8, the rotation angle determination unit 6, the converter 5 and the synchronous motor 1 form a closed loop position control system for controlling the position a of the rotor 3 of the synchronous motor 1 and thus for controlling the mechanical angle of rotation of the motor shaft 2.
For reasons of clarity, FIG. 1 only shows one such individual closed loop position control system. A number of synchronous motors are generally present in a conventional machine, said synchronous motors being activated by means of a respectively assigned driving facility 7 and a respectively assigned closed-loop control device 8. The closed-loop control device 8, driving facility 7, synchronous motor 1, position sensor 4 and the load 10 are thus repeatedly present in a conventional machine, this being indicated by corresponding points in FIG. 1, with only one individual computing apparatus 9 comprising a number of closed-loop control devices, generally being present. In the case of a machine having a number of driving axles, the rotor positions αk of the other synchronous motors are fed to the closed-loop control device 8 in order to synchronize the position of the rotor 3 of the synchronous motor 1 and the position α of the rotor of the synchronous motor is routed to the other closed-loop control devices within the computing apparatus 9, this being shown with a dashed line in FIG. 1.
As already noted at the start, the elements and functionalities shown in FIGS. 1 and 2 are generally known from the prior art and to the person skilled in the art.
One disadvantage of this drive system known from the prior art for operating synchronous motors is that a physically present position sensor, which determines the position α of the rotor of the synchronous motor, must be present in order to operate the synchronous motor. On the one hand, such a position sensor is expensive and on the other hand constitutes a fault source in the event of a malfunction of the position sensor.